The Noble Pen Shell, critically endangered bivalve mollusc that is endemic to the Mediterranean, numbers have drastically decreased in the last few years. The main reason behind this is a contagious parasite outbreak that started in 2016, which stops the shells from closing or slows down the shell closing process. Pen shell populations’ up to date distribution in Turkey, prevalence of the plague and what to do in this situation were discussed in the workshop, which was moderated by the Turkish Marine Research Foundation. At the end of the workshop, contrary to Aegean and Mediterranean Seas, in the Sea of Marmara except for the Strait of Çanakkale it was understood that there weren’t any mass mortalities of the Pen Shell populations. The reason why mass mortalities are not recorded in the Sea of ​​Marmara is considered to be the lack of tolerance of this parasite to low temperature and salinity.

Approximately 50 expert academicians, divers and fishermen from the Marmara Sea, Aegean Sea and the Mediterranean Sea attended the workshop held on September 13, 2020. In the workshop, Pen Shell diseases, Pen Shell population distributions in the Sea of Marmara, Aegean and Mediterranean coasts with their depth distributions and their population status and population changes in the last few years were discussed (Map 1). After these topics, interventions and projects that can be done and their feasibility were discussed.

The Noble Pen Shells live anchored to the seafloor in a partially buried fashion. They can reach up to 120 cm in length and they are known to live for 50 years. Their range is between 0.5 and 60 meters, they feed by filtering detritus and retaining the organic matter. They usually prefer to live in Posidonia oceanica meadows, which is a seagrass species endemic to the Mediterranean. This is because seagrass meadows protect Pen Shells from water current drags and contains detritus.

Map 1: Map of Western Turkey depicting P. nobilis spots. Every spot was marked with regard to the observations of the participants in the workshop. Green dots indicate alive P. Nobilis sightings; red dots indicate dead P. nobilis sightings.

Noble Pen Shells have been used and consumed by humans since the Ancient Egyptian and Roman Empires. In ancient times, people would extract the filaments Pen Shells use to anchor themselves to the seafloor, called byssus filaments, and refine this into a textile material called sea silk. Nowadays, their populations are declining due to pollution, ships anchoring on Pen Shell habitats, trawl fishing and illegal fishing.

Noble Pen Shell numbers saw a drastic decline due to an outbreak in 2016. In fact, since 2019 IUCN updated their conservation status to critically endangered (CR). The reason for this outbreak is a parasite called Haplosporidium pinnae and this parasite is known to kill only Pinna nobilis species. This parasite stops the individuals from closing their shells or slows it down. The parasite impairs the organs that are involved in the shell closing process and leads to the occurrence of infected swollen cysts. In time, severe organ deficiency followed by starvation can be observed.

The parasite affects all Mediterranean countries from Spain to Turkey and the outbreak caused by the parasite should be monitored long-term in our country. We need to take action to circumvent pollution, to stop fishermen from seine fishing on shores where Noble Pen Shells live, and to stop ships from anchoring on seagrass meadows and Noble Pen Shell habitats. Noble Pen Shell, which are under protection in our country, mass mortalities are important for us to understand changes in the ecosystem and for us to predict the changes that may take place thereafter. In the Mediterranean basin, to what extent do Pinna nobilisPinna rudis and Atrina fragilis suffer from this disease is not yet known. Therefore, long-term monitoring in our seas is necessary. On the other hand, in recent years the rise in the water temperatures of the Mediterranean and the possibility that this might be contributing to the parasite’s prevalence is another issue that needs to be investigated.